Mobile wireless communication devices, such as a cellular telephone or a wireless personal digital assistant, can provide a wide variety of communication services including, for example, voice communication, text messaging, internet browsing, and electronic mail. Mobile wireless communication devices can operate in a wireless communication network of overlapping “cells”, each cell providing a geographic area of wireless signal coverage that extends from a radio network subsystem (RNS) located in the cell. The radio network subsystem can include a base transceiver station (BTS) in a Global System for Communications (GSM) network or a Node B in a Universal Mobile Telecommunications System (UMTS) network. Whether idle or actively connected, a mobile wireless communication device can be associated with a “serving” cell in a wireless communication network and be aware of neighbor cells to which the mobile wireless communication device can also associate.
Mobile wireless communication devices can support both voice and data connections, in some cases simultaneously, through radio resources allocated by the radio network subsystem for a radio access portion of the wireless communication network. The voice and data connections can also include paths through circuit switched (CS) and/or packet switched (PS) domains of a core network (CN) that can interconnect the mobile wireless communication device to a public switched telephone network (PSTN) and/or a public data network (PDN). In order for a PS data connection to transmit packets, also known as protocol data units (PDUs), reliably over the radio access portion between the mobile wireless communication device and the wireless communication network, a layer 2 radio link control (RLC) protocol can be used. The RLC protocol can include an “acknowledged” mode that ensures correct delivery of transmitted packets. Unacknowledged packets can be retransmitted by a transmitting end when the packets are received incorrectly by a receiving end. The transmitting end can rely on an acknowledgement (ACK) message or a negative acknowledgement (NACK) message from the receiving end to indicate whether the transmitted packet is correctly received. These ACK/NACK messages can be included with other control information in control messages, such as status PDUs, sent to the wireless communication network from the mobile wireless communication device. In the absence of receiving status PDUs as expected, after a suitable time period, the transmitting end can choose to reset the communication link between the mobile wireless communication device and the radio network subsystem of the wireless communication network by sending a reset control message, such as a RESET PDU, which can be acknowledged by the receiving end by a control message such as a RESET_ACK PDU. The status PDU, RESET PDU and RESET_ACK PDU can form part of a set of RLC control PDUs critical to maintaining a PS data connection. If the RLC control PDUs cannot be transmitted during periods of network congestion, then a PS data connection can be released by the wireless communication network, resulting in an undesirable call drop for the user of the mobile wireless communication device.
During periods with high communication traffic in the radio access portion of the wireless communication network, the radio network subsystem can choose to manage network congestion by allocating a reduced amount of radio resources to the mobile wireless communication device for the PS data connection. PS data connections can be considered non real-time and therefore less critical than real-time CS connections, such as voice calls. When the amount of radio resources allocated is less than required by the mobile wireless communication device to transmit the RLC control PDUs required in the uplink direction for a PS data connection, the PS data connection can be terminated. In addition to the PS data connection, a simultaneous CS data connection between the mobile wireless communication device and the wireless communication network can also be terminated. Network congestion for the packet data connection can inadvertently affect the stability of a circuit switched voice connection.
Thus there exists a need to modify radio link control between the mobile wireless communication device and the radio network subsystem of the wireless communication network during periods of radio access network congestion.